Functional genomic studies on an immune- and antiviral-related gene of MyD88 in orange-spotted grouper, Epinephelus coioides

Abstract

Myeloid differentiation factor 88 (MyD88) is a universal adaptor protein involved in Toll-like receptors and in interleukin-1 receptor-induced nuclear factor-kappaB (NF-κB) activation. In this study, a new MyD88 gene (designated as Og-MyD88) was cloned from orange-spotted grouper, Epinephelus coioides, based on the expressed sequence tag (EST) obtained following Roche 454 GS-FLX™ sequencing. The full-length Og-MyD88 cDNA is composed of 1682 bp and encodes a deduced polypeptide of 289 amino acids with 86% homology to MyD88 of Siniperca chuatsi. The deduced amino acid sequence of Og-MyD88 contains a typical death domain at the amino terminus and a conserved Toll/IL-1R (TIR) domain at the carboxyl terminus, as well as three highly conserved motifs (Box1, Box2 and Box3) within the C-terminal TIR domain. In healthy fish, Og-MyD88 was found to be strongly expressed in immune-related tissues, including the spleen, head kidney, kidney, liver, skin and intestine, with lower expression in heart, stomach, brain and muscle. Transcripts of Og-MyD88 were found to be markedly up-regulated in fish spleen after challenge with Singapore grouper iridovirus (SGIV), a highly lethal viral pathogen to grouper fish. Furthermore, the full length Og-MyD88 and its N-terminal death domain were capable of inducing NF-κB activity in HEK-293 cells. Overexpressed Og-MyD88 showed the ability to inhibit replication of SGIV in grouper spleen (GS) cells. These results suggest that Og-MyD88 is involved in the grouper immune response to invasion of viral pathogens and may share similar functions to those observed in higher vertebrates. © 2012 The Author(s).